There’s nothing anomalous about them. And then it becomes odd to say when a serial killer “blended” in that they must of “manipulated” people. Like maybe they’re not good at “manipulating”, rather they’re just good at what society demands of people and fulfills that role well?

I agree. The manipulation capability of serial killers gets dramatically overrated/mythologized. It's more that they take advantage of obvious vulnerabilities and power imbalances in a pathologically anti-social system that barely deserves to be called a society. And their lack of empathy combined with murderous desires (which is far more easily formed/nurtured within such a violent system) makes it relatively easy for them to decide that taking advantage of these things is a good plan. Some of them are the ones in uniform.

Hell, I recall a story of one serial killer case that a journalist managed to solve like decades(? not certain of the timeline offhand) later and it turned out they had been a cop.